It's been a while since I last saw this (v0.6.6 if I am not mistaken), I love slow-burn games because for me they make way more sense when the characters get together, but I also like to wait until we have at least something sexual starting, so I would like to ask if we can do something with the sister, it does not have to be much, just the initial stuff like touching and kissing.
PS: I know about Sarah but I am mostly interested in the sister only.
No, not yet. It's not compatible with the story line for them to cross that line (part of the reason he asked Sarah out is to stop himself from crossing it, after all). Ignoring a romantic (physical) relationship, I'd say there has been development in the relationship between the main boy and girl.
Sarah story line as indicated in another comment above will end in two more major updates (so ~v0.12.0 in my estimation, as of this moment). The story line for what happens after that is not clear enough yet to give any solid indication on how long this type of content will take, but I imagine it will be in one, or two updates after, since at that point the way they feel about each other is clear to themselves, and all that is left to develop it in a realistic and interesting way. Hopefully, that helps in deciding if you should keep waiting.
On another note, I want to say I really enjoyed how the MC isn't perfect all around and acts selfishly at times. For example, I thought he handled the thing with their mother quite poorly (so far) yet very relatably.
The conversations and general relationship with the landlady is very hard for me. I talked about it in detail in some older post here:
https://f95zone.to/threads/sistersi...-0-fixed-4-i107760.61206/page-30#post-7524006, it's about my thoughts when I was rewriting the conversation to its current state.
Soonish, another conversation with her is happening. It's going to be hard to execute it well, I've written down the basics of it, but it's a scene I'm still very uncertain of. I'm glad to hear you like the story, and thanks for dropping by with your opinion.
As put on my Patreon, I plan to post the next diary page on my Patreon either this Sunday, or the next, at latest.